It is well known in the drafting, graphic arts and signage communities that an ellipse may be described through the use of templates or various devices which employ a slackly-strung non-elastic cord between two fixed focal points. Historically, several devices have been developed which simplify the description of ellipses by providing bases having adjustable means whereby the distance between the focal-points is readily adjustable and variable to accommodate the requirement for the creation of an infinite number of different ellipses having differing conjugate and transverse diameters.
A number of such devices are exemplified in the prior art, such as in the disclosure by Hazen in U.S. Pat. No. 149,474 wherein a wooden base having a sliding adjustable and frictionally lockable member by means of which the distance between the two focal-points or focii may be varied. In U.S. Pat. No. 707,580 Gregory taught a similar method employing a series of spaced-apart holes in an elongated base to provide adjustments to both the distance between the focii and the length of the cord therebetween as well as providing a pivotally mounted roller for a scribing or cutting device. Johnson, in U.S. Pat. No. 768,997 disclosed yet another device having two slidably adjustable and lockable means for varying the inter-focal dimension and provided a spring-loaded means for securing the adjustable end of the inter-connecting cord. Higgins et al., in U.S. Pat. No. 888,709 taught a method of expanding the dimensional capabilities of the preceding devices through the use of extensible tape having means for attachment to the flexible cords of said devices. In U.S. Pat. No. 1,116,549 Berg teaches a method for adjusting the relative conjugate and transverse diameters of ellipses through the utilization of two independent focal-points, each having clutch means for adjusting and maintaining the length of the inter-connecting cord therebetween. Clogston et al,. in U.S. Pat. No. 1,118,900 discloses a method whereby the flexible cord used to encircle the focii is provided with a spool or reel for its storage and locking means to adjust the length of the cord to be used also comprising a rotatable sleeve wherein the pencil or describing means is inserted. In U.S. Pat. No. 1,488,641 Johnston disclosed a device bearing a close resemblance to a vernier caliper, graduated along its length to facilitate adjustment and reduce set-up time. In U.S. Pat. No. 3,224,098 Terrell revealed an ellipse scriber in the form of a beam compass wherein various components are adjustably clamped to a conventional yardstick thereby providing calibrated means to describe ellipses of various configurations. Lastly, Rosenheck, in U.S. Pat. No. 3,947,968 discloses a device, bearing a striking resemblance to the earlier disclosure of Hazen, which has as its principal difference the addition of graduated markings and a cord-follower adapted to accept a marking or scribing instrument.
While all these examples of the prior art possess merit and provide useful and effective means of describing ellipses of various diameters and configurations, it is apparent that none of these inventors have recognized, addressed or anticipated the problem that the present invention is expressly designed to solve.